Image rendering devices such as photocopiers, printers, facsimile machines, and other image producing devices, have been widely used in commerce and industry. Computing devices have also been widely used in commerce and industry. Higher demand for these computing devices has resulted in faster processing speeds that are sufficient for electronically detecting defects in the images rendered by image rendering devices. Detection of image quality defects ensures the production of quality images by image rendering devices.
It may be desirable to take measurements from actual customer documents. This is advantageous in that it avoids the printing of numerous test patterns that would ordinarily be required to acquire information concerning the printing device performance.
There are various existing approaches for detecting image quality defects in images rendered by image rendering devices. In order to detect image quality defects, images rendered by an image rendering device, such as a printer, are captured by an image capturing device, such as a camera, a scanner, or the like, and are compared with synthetic models of the ideal image (e.g., the electronic input image) to detect the existence of an artifact or defect in the printed image. One such system was proposed in U.S. Patent Application Publication No. 2006/0110009, herein incorporated by reference, in its entirety. Due to the full-color information required in these systems, the sensing is performed on post-fused images rather than unfused images (e.g., sensing on the photoreceptor belt or other intermediate image bearing surface). Other systems are known for sensing fused prints, such as printed sheets of paper, such as U.S. patent application Ser. No. 12/109,203, filed Apr. 24, 2008; and Ser. No. 12/018,540, filed Jan. 23, 2008, herein incorporated by reference in their entireties.
In addition, systems exist in which sensors are positioned adjacent to a photoreceptor belt or other image bearing surfaces to detect special test patches and other diagnostic patterns to monitor, diagnose and control IQ problems. One of the advantages of sensing on the photoreceptor belt is that it permits the opportunity to print and sense test-patterns in the inter-document zones (IDZs) or on the normal imaging areas of the belt without making test prints on paper. These are not visible to the customer and do not waste paper.
There are, however, limitations in sensing full color on the photoreceptor belt. For example, since unfused toner is to a large extent opaque, only the top surface can be readily sensed. As such, sensing on the photoreceptor belt can sense substantially only the top-most toner layer of the image.